It is known that closing apps does not help to save battery life. Perhaps, then, Apple should just get rid of the "swipe up to close" feature altogether.
There should be only four possible states for an app. Apple should get rid of the "not running" state and make "suspended" (rather than "not running") the default app state.
Then, all apps should always be listed on the App Switcher in the same order as on the Home Screen, going from left to right, top to bottom, page to page, and not going through the bottom row of apps (which, on an iPhone, defaults to showing Phone, Safari, Messages, and Music) until after the last app on the last page. This effectively makes the App Switcher a "flattened" version of the Home Screen. Also, if you rearrange apps on the Home Screen or hit on "Reset Home Screen Layout" from the settings, the corresponding rearrangement should automatically happen to the App Switcher as well. Finally, if you install a new app, or reinstall one that you have previously deleted, then it should automatically start to initialize to the "suspended" state and then appear on the App Switcher in the right position depending on where the newly installed app is placed on the Home Screen.